High voltage liquid-filled bushing



Nov. 16, 1937. TERPAK HIGH VOLTAGE LIQUID FILLED BUSHING Filed June 30, 1937 drill r/WW7 Attorrw ey.

Irv verw tor:

5 Stephen TeTpak,

Patented Nov. 16, 1937 UNITED STATES PATENT OFFICE men VOLTAGE LIQUID-mum nusnmo Stephen Terpak, Plttsfield, Mala, animala General Electric Company, a corporation of New York My invention relates to high voltage liquidfilled bushings. A bushing 01 this type commonly includes a conductor surrounded by a casing or housing filled with an insulating liquid and pro- 5 vided with an expansion chamber, the liquid extending into a partly filled expansion chamber to permit thermal expansion and contraction of the liquid. The expansion chamber commonly communicates with the outside air to prevent excessive pressure within the bushing and expansion chamber when the liquid is fully expanded. Whenever the temperature of the liquid decreases, however, some outside air is drawn into the expansion chamber and this air frequently 15 contains moisture which may be absorbed by the liquid and seriously reduce its dielectric strength.

The usual expansion chamber is a glass globe or cylinder mounted on the outer end oi! the bushing.

It has been suggested that this expansion chamexclude outside air with its moisture and still permit the necessary expansion of the insulating liquid without excessive increase of pressure in the bushing and expansion chamber. An ex- 15 pansion chamber large enough for this purpose,

however, would be objectionable.

The general object of the present invention is to provide an improved liquid-filled bushing in which the space above the liquid in the expansion ;0 chamber communicates freely with a sealed space within the main body of the bushing so that the expansion chamber may be 01' normal size and full thermal expansion of the liquid may occur without producing excessive pressure.

35 The invention will be better understood from the following description taken in connection with the accompanying drawing in which Fig. 1 is a view of a high voltage liquid-filled bushing constructed in accordance with the invention;

40 Fig. 2 is a view partly in section and with parts broken away of the bushing shown in Fig. 1; and

Fig. 3 is a sectional view of a modified form of the lower or inner end of the bushing.

The high voltage bushing shown in Figs. 1 and 2 includes a central or axial conductor I I! extending through and surrounded by a conductive tube II, the conductor III and tube II being connected to an outer terminal I2. The conductor I0 and tube I I are surrounded by a casing or housing in- 50 eluding an outer porcelain section I3, an inner porcelain section I4 and an intermediate connecting metal section I5. The bushing is mounted through an opening IS in a support I! which may be the cover 01' the casing oi. a transformer or other electrical apparatus. The bushing is ber be large enough so that it may be sealed tov supported by a flange I8 resting on the support I1. The bushing is filled with an insulating liquid I9 which extends through a pipe 2| into an expansion chamber 2| mounted on the outer or upper end 01' the bushing, the liquid partly filling the expansion chamber so as to leave a space 22 above the upper surface of the liquid. The expansion chamber 2I is tightly sealed to exclude outside air and moisture.

The conductor I0 and tube II are surrounded m by a second conductive tube 23 which is concentrically spaced from thetube II to enclose a space 24. This space 24 communicates through a pipe 25 with the space 22 above the insulating liquid III in the expansion chamber 2|. The spaces 22 and 24 are filled with any suitable gas which may be dry air but which is preferably some inert gas such as dry nitrogen. The tube 23 is of course sealed at its upper and lower ends to the inner tube I I by annular seals 26. A drain pipe 21 normally closed by a plug 28 may be provided to permit any liquid incidentally found in the space 24 to be withdrawn. Cylindrical insulating barriers 29 may be provided between the tube 23 and the metal section I! of the casing which is of course normally at ground potential. The outer tube 23 is preferably 01' conductive material and is conductively connected to the inner tube I I and the conductor II so that its potential is always the same as that of the con- 30 duetor.

Any increase in the temperature oi the surrounding air or any heat reaching the insulating liquid I! from the electrical apparatus with which the bushing is associated will cause the liquid to expand and its level to rise in the expansion chamber 2|. This will compress the gas in the upper part of the expansion chamber but this gas can expand into the space 24 inside the tube 2: within the body of the bushing. The space 24 may obviously be made large enough to prevent excessive pressure within the expansion chamber 2| at all times and particularly when the liquid I9 is at its maximum temperature and has risen to its maximum level in the expansion chamber. The upper end 01 the pipe 25 which provides communication between the gas space 22 in the expansion chamber and the space 24 inside the outer tube 23 should extend well above the highest level ever reached by the liquid I9 in the expansion chamber 2I so that this liquid can never enter the space 24 through this tube 25. In addition to providing additional expansion space for the gas above the liquid in the expansion chamber 2|, the diameter of the conductive tube 23 is of course considerably larger than that of the inner tube It and the curvature of the surface is consequently not so great so that the tube 23 has the incidental advantage that the voltage applied to the terminals of the bushing may be very high without danger of corona.

As shown in Figs. 1 and 2, the inner tube l l and. the outer tube 23 are connected at their upper ends to the terminal l2 of the bushing so that these parts are always at the same potential. The lower or inner ends of the tubes I I and 23 are not connected, however, to the conductor it] so that these tubes do not carry any of the current flowing between the terminals of the bushing. A modified form of the invention is indicated in Fig. 3 in which the conductor l0 and tubes H and 23 are all conductively connected together at the lower or inner end of the bushing. The conductor in and tubes I land 23 are therefore all connected in parallel between the two terminals of the bushing so that the conductor it) does not have to carry all the current.

The invention has been explained by describing a particular bushing construction and a modification thereof, but it will be apparent that changes may be made without departing from the spirit of the invention and the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high voltage bushing including a casing surrounding a conductor, an expansion chamber at one end of the casing, an insulating liquid in the casing and extending into and partly filling the expansion chamber, an expansion chamber within said casing and communicating with the space above the liquid in the other expansion chamber, and a gas in said expansion chambers,

aoeaeec said expansion chambers being sealed from the outside air.

2. A high voltage bushing including a casing surrounding a conductor, an expansion chamber at one end of the casing, an insulating liquid in the casing and extending into and partly filling the expansion chamber, an expansion chamber within said casing and concentrically surrounding the conductor, said latter expansion chamber communicating with the space above the liquid in the other expansion chamber, and a gas in said expansion chambers, said expansion chambers being sealed from the outside air.

3. A high voltage bushing including a casing surrounding a conductor, an expansion chamber at one end of the casing, a tube surrounding the conductor, an insulating liquid surrounding the tube in the casing and extending into and partly filling the expansion chamber, a space within said tube being sealed. from the liquid and communicating with the space above the liquid in said expansion chamber, and a gas in said space and in the space above the liquid in the expansion chamber, said space and expansion chamber being sealed from the outside air.

4. A high voltage bushing including a casing surrounding a conductor, an expansion chamber at one end of the casing, two tubes surrounding the conductor and concentrically spaced from each other, an insulating liquid surrounding the outer tube in the casing and extending into and partly filling the expansion chamber, the space between the tubes being sealed from the liquid and communicating with the space above the liquid in the expansion chamber, and a gas in said space and in the space above the liquid in the expansion chamber, said space and expansion chamher being sealed from the outside air.

STEPHEN TERPAK. 

